Speed of light

paul becke · Mar 14, 2017

tansy said:
Nor slow down? Even infinitesimally?

I have read some years ago that two researchers at an American college (one, I think, of Scandinavian descent), had discovered - certainly postulated - that there is evidence that light does slow down infinitesimally as it passes a planet - I believe it said, under the influence of gravity though my memory of it is not too clear.

However, there are aspects of light that seem to confirm the spirtual wisdom of many mainstream religions in valorising light so enromously, even to the point of apotheosis. Well, in one of the prayers in our Catholic Book of Hours, we invoke God as the 'true light' and 'source of light'. I realise its role in agriculture and the survival of all creation, however little understood, would have been a factor, as well.

What intrigues me is that its speed being absolute when measured by an Observer, either stationary or travelling at a constant speed, in the same direction, means that its origin must be non-local, a different reference-frame... outside of our universe of space-time. Indeed, that non-locality is true of all subatomic particles, apparently.

However, by far the strangest phenomenon associated with light is surely that extrapolated from quantum mechanics, to the effect that the light from a distant star must have 'known' (more like the agency behind it) that an Observer of it was there to see it. In fact, there is an experiment whereby an Observer decides which way round a planet in its path the beam of a light from a distant star will travel : on the left side or the right (don't know about up or down !), AFTER it set out on its journey !!!!! Crazy stuff, but I believe I have described the phenomena correctly.

As regards the constancy of the speed of light, I doubt if there is any chance of the text books changing the long-received calculation of the absolute speed of light. Tansy.

xianghua · Mar 14, 2017

tansy said:
Nor slow down? Even infinitesimally?

actually in the beginning of the universe its speed up above the speed of light:

Inflation (cosmology) - Wikipedia

paul becke · Mar 14, 2017

tansy said:
Oh my goodness, I knew my questions were simplistic . Um, what is 'free space'? I've never heard of that.
This is the trouble when I ask questions, it always leads to a thousand more...I do wish I could have done more physics at school. And it never seemed that I had chance to ask thequestions I wanted to know

Photons constitute the light, Tansy.

Paul of Eugene OR · Mar 14, 2017

Oscarr said:
Question: If you were driving your motor vehicle at the speed of light and you turned your headlights on, would they work?

The relativity formulas for motion and time dilation assure us that if you were actually traveling at the speed of light you would not experience the passing of time at all, so you could not change the state of your headlights, which takes a little bit of time. But if you were only traveling 99.99 percent of the speed of light, and you turned on your headlights, you would, yourself, perceive the light to go out from your headlights at the regular speed of light. Those on earth would also deduce, after taking into account all the observations, a light traveling from your vehicle at the speed of light as measured from earth. Earthlings would account for your observation of the speed of light by noting your squashed length and your retarded time due to the effects of motion near the speed of light.

Light is always measured at the same speed by anyone who measures it regardless of their state of motion.

tansy · Mar 14, 2017

Archie the Preacher said:
As with many things, it depends.

The speed of light - "c", as it is abbreviated - is normally cited for velocity as being in a vacuum as (according to Wiki) 299,792,458 meters per second; or about 186,282 miles per second. It does slow down in various 'mediums' like glass, atmosphere or water.

So yes, it does slow down at times in various materials allowing transmission. (Obviously, it slows down a lot on concrete or steel.)

However, it does not slow down by running out of energy. It is going just as fast coming from another galaxy as it does from the Sun.

Nor does the form of 'generation' make any difference. For instance, when a baseball is thrown by a person, it has a specific velocity. If the person throwing is standing (with suitable safety devices) in the bed of a moving pickup truck and throwing in the direction of travel, the ball will be moving (relative to the ground) at a combined velocity of the thrower and the truck.

That doesn't happen with light. If the person in the prior paragraph turns on a forward facing flashlight in the moving truck, the light coming from the flashlight is still moving at the speed of light, not the speed of light PLUS the speed of the truck.

The reason for that is the subject of PhD papers on "Relativity". In short, velocity alters time; the speed of light alters time a lot.

If you are really curious, learning more about it is a life long hobby.

Thank you. Yes, I did wonder whether things could slow light down. Because from what I understand, the photons move along wave lengths, so surely wave lengths can be alktered (like when you throw a stone in a pond or go faster or slower in aboat, the wave lengths (and heights, I suppose) would alter.
Of course, the trouble is with me, is that if I start to look something up to get information, there is so much other info I then have to research and look up (including terminology), it gets difficult. Quite a while ago, I looked up some stuff about forms of energy, I think it was...and it was so much more complex than what we were simplistically taught at school. It's frustrating because I find all this stuff fascinating and I like thinking about it - but obviously I do not have the time to do a whole school and then university course on physics! let alone the maths that is involved!

And then, you mention time! I reckon time is just an illusion really that we hook things up onto for convenience..that is, it's more of a concept than anything else. I did get a book out of the library about time, but unfortunately it was due back before I had a chance to finish reading it.

tansy · Mar 14, 2017

paul becke said:
Photons constitute the light, Tansy.

Thanks

tansy · Mar 14, 2017

xianghua said:
actually in the beginning of the universe its speed up above the speed of light:

Inflation (cosmology) - Wikipedia

Yes, I thought I'd heard something like that before

lesliedellow · Mar 14, 2017

tansy said:
And then, you mention time! I reckon time is just an illusion really that we hook things up onto for convenience..that is, it's more of a concept than anything else. I did get a book out of the library about time, but unfortunately it was due back before I had a chance to finish reading it.

Time as an illusion runs foul of the fact that you can invariably remember yesterday, and, just as invariably, you can't remember tomorrow.

Armoured · Mar 14, 2017

Oscarr said:
Question: If you were driving your motor vehicle at the speed of light and you turned your headlights on, would they work?

Relative to you they would.

Armoured · Mar 14, 2017

lesliedellow said:
Time as an illusion runs foul of the fact that you can invariably remember yesterday, and, just as invariably, you can't remember tomorrow.

MAybe we can remember yesterday because we're looking towards it, but can't remember yesterday because we're looking away from it? You tend to look in the direction you're traveling.

Think about it.

John 1720 · Mar 14, 2017

tansy said:
The other day my husband was trying to remember the formula for working out something like velocity or acceleration over a certain distance at so many miles per hour (or something like that) re a particular motor-bike.

Anyhow, it made me wonder about the speed of light. My question is, is the speed of light constant, or does it accelerate.
For example when light comes from the sun, as it is 'ejected' so to speak, does it gather speed until it reaches a constant?
Also when light hits something and maybe is absorbed or rebounds somewhat, does that slow it down?

Sorry, I'm sure this is a very simplistic question and absolutely shows my lack of knowledge of these things...I'm not even posing the question in the right terms, probably, but I hope you understand what I'm querying.

It is constant in a vacuum but slows down when encountering resistance such as light through water or a crystal.

This may help

Slowing the Speed of Light to Zero

Actually MIT invented a way to pictorial capture a trillion frames per second which have applications to using light like we use ultrasound today.

tansy · Mar 14, 2017

lesliedellow said:
Time as an illusion runs foul of the fact that you can invariably remember yesterday, and, just as invariably, you can't remember tomorrow.

Ah, true. Maybe I meant to say something more like, the way we measure time is an illusion...that is time varies according to your viewpoint..you know Starship Enterprise, star date 6973 kind of thing. If you lived on Saturn, time would be measured differently. Is there, for example, an absolute time reference?

tansy · Mar 14, 2017

John 1720 said:
It is constant in a vacuum but slows down when encountering resistance such as light through water or a crystal.

This may help

Slowing the Speed of Light to Zero

Actually MIT invented a way to pictorial capture a trillion frames per second which have applications to using light like we use ultrasound today.

Wow, thats amazing .

lesliedellow · Mar 14, 2017

Armoured said:
MAybe we can remember yesterday because we're looking towards it, but can't remember yesterday because we're looking away from it? You tend to look in the direction you're traveling.

Think about it.

If time was an illusion, it wuldn't have an existence outside of your brain, and it wouuldn't havee aany hard and fast properties, such as being a one way streett.

lesliedellow · Mar 14, 2017

tansy said:
Ah, true. Maybe I meant to say something more like, the way we measure time is an illusion...that is time varies according to your viewpoint..you know Starship Enterprise, star date 6973 kind of thing. If you lived on Saturn, time would be measured differently. Is there, for example, an absolute time reference?

There is an absolluute time in the sense that everybody would measure the age of the universe to be 13.8 billion years.

tansy · Mar 14, 2017

lesliedellow said:
If time was an illusion, it wuldn't have an existence outside of your brain, and it wouuldn't havee aany hard and fast properties, such as being a one way streett.

Yes, but they are talking now aren't they, that perhaps we could see or travel back into the past, also that time curves..haven't looked into this really. I'm actually not totally convinced it is a one way street..depending on how one views it. Haven't got time to think that through properly at the moment as I have to go and pick my husband up in a couple of minutes

lesliedellow · Mar 14, 2017

tansy said:
Yes, but they are talking now aren't they, that perhaps we could see or travel back into the past, also that time curves..haven't looked into this really. I'm actually not totally convinced it is a one way street..depending on how one views it. Haven't got time to think that through properly at the moment as I have to go and pick my husband up in a couple of minutes

There have been some theoretical designs for time machines which could travel into the past, but hugely speculative. And there are the obvious logical problems involved, such as travelling back to a time before you were born, and shooting your mother, or (even worse) travelling back to an earler time in your life, shooting yourself, and then standing trial for murdering yourself.

Archie the Preacher · Mar 14, 2017

tansy said:
Of course, the trouble is with me, is that if I start to look something up to get information, there is so much other info I then have to research and look up (including terminology), it gets difficult.

Ohhhh, you betcha Red Ryder! The more one studies anything, the more that particular 'anything' become linked to 'everything'.

tansy said:
And then, you mention time!

The easiest way to think of time is as the 'passing of events'. And the 'direction' of time is determined by entropy. (Just when you thought things couldn't get weirder!)

Look up "Planck Time" when you have half an hour or so to kill.

toLiJC · Mar 14, 2017

tansy said:
The other day my husband was trying to remember the formula for working out something like velocity or acceleration over a certain distance at so many miles per hour (or something like that) re a particular motor-bike.

Anyhow, it made me wonder about the speed of light. My question is, is the speed of light constant, or does it accelerate.
For example when light comes from the sun, as it is 'ejected' so to speak, does it gather speed until it reaches a constant?
Also when light hits something and maybe is absorbed or rebounds somewhat, does that slow it down?

Sorry, I'm sure this is a very simplistic question and absolutely shows my lack of knowledge of these things...I'm not even posing the question in the right terms, probably, but I hope you understand what I'm querying.

the speed of such things depends not only on the constancy that God put in(to) it but also on whether the forces of the "Light" and the "darkness" change it, albeit for a while and in particular cases, which already happened - even scientists managed to slow down the speed of light

Blessings

lesliedellow · Mar 14, 2017

toLiJC said:
the speed of such things depends not only on the constancy that God put in(to) it but also on whether the forces of the "Light" and the "darkness" change it, albeit for a while and in particular cases, which already happened - even scientists managed to slow down the speed of light

Blessings

Nobody can slow down the speed of light, except by passing it through something like glass or water, anymore than they can tweak gravity to whatever value they want it.

Speed of light

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